I noticed that many non-natives have a hard time hearing/distinguishing the short "i" sound at the end of some pluralized words, and many Duo learners call it "silent", when in fact it isn't. That's why I used quotes in my post above.
So the answer is that it's not really silent, it's just that the pronunciation is similar to the singular form.
This is one of those situations where it's best to hear the difference between a word's singular and plural forms, as pronounced by the same person. Open this link: https://forvo.com/user/potestasity/pronounced-words/ and click on the listen buttons for the following words:
- taur (bull) - It has two syllables: tá-ur.
- tauri (bulls) - It has that short "i" sound at the end, and the word still has only two syllables: tá-uri.
- taurii (the bulls) - It has a normal "i" sound at the end, which is long enough to make the word have three syllables: tá-u-rii.
Notice how the short "i" sound is almost whispered in tauri, you basically stop using your vocal cords ~right-before-or-during pronunciation of the vowel "i", so you use only the exhaled air to pronounce it.
Contrast that to the normal "i" sound in taurii, which is a bit longer, and for which you use both the vocal cords and the exhaled air to pronounce the vowel "i".